docs: Recommend newer version of "sparse".

The previously recommended version of sparse, version 0.4.4, does not
support -Wsparse-error properly, so configuring with --enable-Werror and
--enable-sparse will not have the desired effect of breaking the build
when sparse reports an error.  Version 0.5.1 and later do implement this
properly.

This commit also updates the recommended URL for sparse because the
previous URL doesn't have the newer releases.

Reported-by: Justin Pettit <jpettit@ovn.org>
Signed-off-by: Ben Pfaff <blp@ovn.org>
Acked-by: Justin Pettit <jpettit@ovn.org>

Documentation/intro/install/general.rst

@@ -160,8 +160,8 @@ other than plain text, only if you have the following:
 If you are going to extensively modify Open vSwitch, consider installing the
 following to obtain better warnings:
 
-- "sparse" version 0.4.4 or later
-  (https://www.kernel.org/pub/software/devel/sparse/dist/).
+- "sparse" version 0.5.1 or later
+  (https://git.kernel.org/pub/scm/devel/sparse/sparse.git/).
 
 - GNU make.